The present invention relates generally to wireless communication systems and, more particularly, to a method for performing an automatic repeat request (ARQ) in mobile communication systems.
Wireless communication systems, such as mobile communication systems, use automatic repeat request (ARQ) techniques to detect severely degraded communication channel conditions and to avoid waste of communication link capacity. FIG. 1 shows a conventional mobile communication system 102 using an ARQ technique. The conventional mobile communication system 102 includes a transmitter 104 and a mobile communication device 106. The ARQ technique uses feedback messages, such as acknowledgement (ACK) and non-acknowledgement (NACK) messages to report failed transmissions. Examples for ARQ mechanisms operating over wireless channels include Radio Link Control (RLC) protocols, Hybrid ARQ (HARQ) protocol and the like.
The transmitter 104 transmits a stream of data packets 108 to the mobile communication device 106. Each transmitted data packet, such as data packet 110, includes a sequence number (SN) 112. The mobile communication device 106 receives the stream of data packets 108. For non-received data packets, the mobile communication device 106 communicates NACK SNs 114 to the transmitter 104. The transmitter 104 receives the NACK SNs 114 and attempts retransmission of the non-received data packets associated with these NACK SNs 114.
Mobile communication systems operating according to long term evolution (LTE) standards use selective, repeat ARQ techniques. Using these techniques, the mobile communication device 106 accumulates the NACK SNs and communicates the list of accumulated NACK SNs to the transmitter 104 at regular time intervals, for retransmission. Each NACK SN is stored in the transmitter 104. FIG. 2 shows the transmitter 104, which includes a plurality of counters 202a-202d for storing the NACK SNs 114.
LTE communication standards typically use a 1024-NACK SN and a 512-NACK SN format for performing selective, repeat ARQ. In the 1024-NACK SN format, the mobile communication device 106 accumulates a list of 1024 NACK SNs and communicates the list to the transmitter 104. In the 512-NACK SN format, the mobile communication device 106 accumulates a list of 512 NACK SNs and communicates the list to the transmitter 104. Using suitable techniques such as a half-window technique, 512 counters are required in the transmitter 104 to store 1024 NACK SNs, while 128 counters are required in the transmitter 104 to store 512 NACK SNs. This considerably increases the processing headroom of the transmitter 104, thereby increasing processing time.
It would be advantageous to have a wireless communication system using selective, repeat ARQ technique with reduced processing headroom and reduced processing time.